Wireless radio frequency (“RF”) communications systems, such as cellular communications systems, WiFi networks, microwave backhaul systems and the like, are well known in the art. Some of these systems, such as cellular communication systems, operate in the “licensed” frequency spectrum where use of the frequency band is carefully regulated so that only specific users in any given geographical region can operate in selected portions of the frequency band to avoid interference. Other systems such as WiFi operate in the “unlicensed” frequency spectrum which is available to all users, albeit typically with limits on transmit power to reduce interference.
Cellular communications systems are now widely deployed. In a typical cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells,” and each cell is served by a base station. The base station may include baseband equipment, radios and antennas that are configured to provide two-way RF communications with fixed and mobile subscribers that are positioned throughout the cell. The base station antennas generate radiation beams (“antenna beams”) that are directed outwardly to serve the entire cell or a portion thereof. Typically, a base station antenna includes one or more phase-controlled arrays of radiating elements, which are commonly referred to as phased array antennas.
There has been a rapid increase in the demand for wireless communications, with many new applications being proposed in which wireless communications will replace communications that were previously carried over copper or fiber optic communications cables. Conventionally, most wireless communications systems operate at frequencies below 6.0 GHz, with a few notable exceptions such as microwave backhaul systems, various military applications and the like. As capacity requirements continue to increase, the use of higher frequencies is being considered for many applications, including frequencies in both the licensed and unlicensed spectrum. As higher frequencies are considered, the millimeter wave spectrum, which includes frequencies from approximately 25 GHz to as high as about 300 GHz, is a potential candidate, as there are large contiguous frequency bands in this frequency range that are potentially available for new applications. The use of cellular technology has also been contemplated for so-called “fixed wireless access” applications such as connecting cable television or other optical fiber, coaxial cable or hybrid coaxial cable-fiber optic broadband networks to individual subscriber premises over wireless “drop” links. There currently is interest in potentially deploying communications systems that operate in the 28 GHz to 60 GHz (or even higher) frequency range for such fixed wireless access applications using fifth generation (“5G”) cellular communications technology.
For many fifth generation (5G) cellular communications systems, full two dimensional beam-steering is being considered. These 5G cellular communications systems are time division multiplexed systems where different users or sets of users may be served during different time slots. For example, each 10 millisecond period (or some other small period of time) may represent a “frame” that is further divided into dozens or hundreds of individual time slots. Each user may be assigned one of the time slots and the base station may be configured to communicate with different users during their individual time slots of each frame. With full two dimensional beam-steering, the base station antenna may generate small, highly-focused antenna beams on a time slot-by-time slot basis as opposed to a constant antenna beam that covers a full sector. These highly-focused antenna beams are often referred to as “pencil beams,” and the base station antenna adapts or “steers” the pencil beam so that it points at different users during each respective time slot. Pencil beams may have very high gains and reduced interference with neighboring cells, so they may provide significantly enhanced performance.
In order to generate pencil beams that are narrowed in both the azimuth and elevation planes, it is typically necessary to provide antennas having a two-dimensional array that includes multiple rows and columns of radiating elements with full phase distribution control. The antennas may be active antennas that have a separate transceiver (radio) for each radiating element in the planar array (or for individual sub-groups of radiating elements in some cases) to provide the full phase distribution control (i.e., the transceivers may act in coordinated fashion to transmit the same RF signal during any given time slot, with the amplitude and/or phase of the sub-components of the RF signal output by the different transceivers manipulated to generate the directional pencil beam radiation pattern). While this technique can provide very high throughput, the provision of planar array antennas and large numbers of individual transceivers may add a significant level of cost and complexity.